JP4044503B2 - Pulse light source for communication - Google Patents

Description

  The present invention relates to a pulse light source for communication that includes a semiconductor laser and a Fabry-Perot electro-optic modulator and generates an optical pulse.

  Conventionally, there is a pulse laser as a device for generating an optical pulse (see Non-Patent Document 1). In a pulse laser, an optical pulse train is generated by a laser medium inserted in a laser resonator and having a light amplification function, a band of a band pass filter, and a mechanism in which light intensity is modulated at a specific time period called mode lock. The pulse width and repetition frequency of the optical pulse train are determined by the laser resonator, and a short optical pulse can be generated by high-speed light intensity modulation using a broadband laser medium and mode locking.

  Conventionally, as a method for modulating the pulse width of an optical pulse, there is a method of using a short optical pulse having a broadband optical frequency component, making the pulse incident on an optical bandpass filter, and modulating the transmission band of the filter. .

  As another means capable of generating an optical pulse, a Fabry-Perot electro-optic modulator using an electro-optic modulator is known (see Non-Patent Document 2). This Fabry-Perot electro-optic modulator has a structure in which an optical phase modulator is inserted into an optical resonator, and generates an optical pulse train by inputting laser light into the optical resonator and inputting microwaves into the optical phase modulator. be able to.

  FIG. 13 shows a configuration of a pulse light source including a conventional Fabry-Perot electro-optic modulator. In the figure, 11 is a microwave generator for generating microwaves, 14 is a semiconductor laser, 15 is an isolator having a function of removing return light, 16 and 18 are a pair of mirrors constituting a Fabry-Perot optical resonator, and 17. Is an optical phase modulator inserted between the pair of mirrors.

Thus, the Fabry-Perot electro-optic modulator has a structure in which the optical phase modulator 17 is inserted into the Fabry-Perot optical resonators 16 and 18. When a CW (continuous-wave) laser beam (a laser beam that oscillates continuously in time) is input to the Fabry-Perot electro-optic modulator, a 2 × fm optical pulse train is generated, and the pulse width is expressed by the following equation (1): It depends on.
1 / (2F fm β) (1)
Here, F: finesse (sharpness) of the Fabry-Perot optical resonator, fm: modulation frequency, β: modulation index of the optical phase modulator 17. For example, if F = 50, β = 0.25, and fm: 40 GHz, a pulse train having a pulse width of 1 ps and a repetition frequency of 80 GHz as shown in FIG. 14A can be generated.

  FIG. 14B shows the relative phase of the light pulse shown in FIG. 14A with respect to the incident light. From the figure, it can be seen that the phase of the light greatly fluctuates with the generation of the optical pulse. Considering that it is equivalent that the frequency of light changes when the phase of light changes, an optical pulse generated at a timing such as the value of time × fm is 0.5, 1.5, 2.5, etc. That is, the frequency of the optical pulse is repeatedly shifted positively or negatively with the optical pulse generated at the timing when the value of time × fm is 1, 2, 3, or the like. Explaining this phenomenon in terms of wavelength, the optical pulse generated by the Fabry-Perot electro-optic modulator is shifted from the wavelength of the incident light to the longer wavelength side and from the shorter wavelength side to the shorter wavelength side. The repeated light pulses are repeated alternately.

  Since the pulse width of the optical pulse generated by the Fabry-Perot electro-optic modulator is inversely proportional to the modulation index β from the above equation (1), the output of the microwave driving the optical phase modulator 17 is changed, The pulse width can be made variable by changing the modulation index β. For example, if F = 120 and fm = 10 GHz, the modulation index β can be changed from 0.25 to 0.04, and the pulse width can be varied from 1 ps to 10 ps or more as shown in FIG. . The modulation index β is a value indicating the degree of phase modulation by the EO effect (electro-optic effect), and is proportional to the drive voltage of the optical phase modulator 17.

T. Morioka, K. Okamoto, M. Ishii and M. Saruwatari “Low-noise, pulsewidth tunable picosecond to femtosecond pulse generation by spectral filtering of wideband supercontinuum with variable bandwidth arrayed-waveguide grating filters” ELECTRONICS LETTERS 25th April 1996 Vol.32 No.9 pp. 836-837 G. M. Macfarlane, A. S. Bell, E. Riis, and A. I. Ferguson “Optical comb generator as an efficient short-pulse source” OPTICS LETTERS Vol. 21, No. 7, April 1, 1996 pp. 534-536

  However, since the pulse width of the conventional pulse laser is determined by the laser medium, the band of the band-pass filter, and the mode lock method, it is difficult to modulate the pulse width of the output light stably and at high speed.

  In addition, the conventional method of modulating the pulse width of an optical pulse by using a short optical pulse having a broadband optical frequency component, entering the pulse into an optical bandpass filter, and modulating the transmission band of the filter is as follows: Since it is difficult to modulate the transmission band continuously at high speed, it is difficult to modulate the optical pulse width at high speed.

  On the other hand, the conventional Fabry-Perot electro-optic modulator can modulate the optical pulse width at a high speed, but the optical pulse train generated from the Fabry-Perot electro-optic modulator has the wavelength of the incident light to the Fabry-Perot electro-optic modulator. On the other hand, since the optical pulse whose wavelength is shifted to the long wavelength side and the optical pulse whose wavelength is shifted to the short wavelength side are alternately repeated, the propagation characteristics of the optical pulse are adjacent when passing through an optical fiber having chromatic dispersion. Because of the difference between matched pulses, the optical pulse train has shifted in pulse timing after passing through the fiber as shown in FIG.

  In addition, when an optical pulse train generated by a conventional Fabry-Perot electro-optic modulator is passed through an optical amplifier, the amplification characteristics of the optical pulse differ between adjacent pulses, so that the intensity of the pulse is modulated as shown in FIG. It has been added.

  In addition, when a conventional Fabry-Perot electro-optic modulator is connected to an optical fiber using an optical connector for communication, reflection from the connection point or Brilliant scattering generated in the optical fiber causes the output from the output side. Since the optical resonance state becomes unstable due to the recombination of the return light with the Fabry-Perot electro-optic modulator, the optical pulse train generated by the Fabry-Perot electro-optic modulator can be used for optical communication propagating over an optical fiber over a long distance. There wasn't.

The present invention has been made to solve the above-described problems, and its purpose is as follows.
(1) Provide a communication pulse light source capable of high-speed pulse width modulation.
(2) To provide a pulse light source for communication in which the timing and intensity of an optical pulse do not change even through an optical fiber having wavelength dispersion and an optical amplifier having a frequency dependence on gain characteristics.
(3) Provide a pulse light source for communication that does not become unstable due to return light.
There is.

In order to achieve the above object, a communication pulse light source of the present invention is a pulse light source composed of a semiconductor laser and a Fabry-Perot electro-optic modulator, and a modulation microwave that drives the Fabry-Perot electro-optic modulator. varied according to the voltage amplitude of the control signal, to have a pulse width varying means capable of a pulse width of the light output variable, the pulse width varying means is a microwave input side of the Fabry-Perot electro-optic modulator A variable microwave attenuator provided, the variable microwave attenuator including an input side diode switch having at least n outputs (n is an integer of 2 or more), an output side diode switch having at least n inputs, It is possessed and n each attenuation of different fixed microwave attenuator connected to each channel of which switches between diode switch It is characterized in.

Here, the output light in which the instantaneous optical frequency of the output light pulse of the pulsed light source is repeatedly shifted positively or negatively compared to the input optical frequency every other output pulse train is shifted by a certain frequency, Or it can be characterized by having a frequency adjusting means for making optical output without frequency shift.

Further, the frequency adjusting means is provided on the light output side of the Fabry-Perot electro-optic modulator, and can pass only the long wavelength side or the short wavelength side with respect to the wavelength of the incident light, and has a wavelength selectivity. It can be characterized by being a variable optical filter or an optical bandpass filter.

Further, the output optical pulse train of the pulse light source, it is possible that optical frequency components by separating, characterized by having a constant frequency shift or frequency adjusting means to two or more light output without the frequency shift, .

  Further, the frequency adjusting means is an arrayed waveguide grating provided on the light output side of the Fabry-Perot electro-optic modulator and capable of passing only the long wavelength side or the short wavelength side with respect to the wavelength of the incident light. Can be characterized.

  In addition, the frequency adjusting means includes a light intensity modulator provided on the light input side or light output side of the Fabry-Perot electro-optic modulator, and the light intensity in synchronization with the modulation of the Fabry-Perot electro-optic modulator. And a phase modulator for adjusting the phase of the modulator.

And a frequency adjusting unit that transmits only an optical frequency component that is an even multiple of 2 or more of a modulation frequency in the Fabry-Perot electro-optic modulator, and that makes a repetition frequency of an optical output pulse an even multiple of 2 or more of the modulation frequency. Can be characterized.

  The frequency adjusting means may be an optical interferometer provided on the light output side of the Fabry-Perot electro-optic modulator.

  And a return light blocking means provided on the light output side of the Fabry-Perot electro-optic modulator and functioning so that a return light component of the light output does not recombine with the Fabry-Perot electro-optic modulator. can do.

  Further, the return light blocking means has a direction dependency of transmittance, and has high transmittance only in the output direction, an isolator, an optical filter, or an output-side end face of an optical resonator of the Fabry-Perot electro-optic modulator The return light is structured so as not to be recoupled to the optical resonator.

  With the above configuration, according to the present invention, it is possible to realize a pulse light source for communication capable of high-speed pulse width modulation that cannot be realized by the prior art.

  In addition, when an optical pulse train generated by a conventional Fabry-Perot electro-optic modulator is passed through an optical fiber having chromatic dispersion, not only the optical pulse timing is shifted, but also the intensity between adjacent optical pulses can be passed through an optical amplifier. However, according to the present invention, since the problem is solved according to the present invention, it can be applied to communication.

  Conventionally, when an optical connector is used for communication to connect to an optical fiber, return light is generated from the output side due to reflection at the connection point or Brilliant scattering generated in the optical fiber. In order to make it unstable, the optical fiber cannot be used for optical communication propagating over a long distance. However, according to the present invention, the problem is solved, and the optical fiber can be used for optical communication propagating over a long distance.

  Furthermore, according to the present invention, it is possible to generate a multi-wavelength pulse train with one light source and to stably generate a pulse train having an even multiple of the modulation frequency. The application range can be expected to expand.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 shows a configuration example (first embodiment) of a communication pulse light source including a Fabry-Perot electro-optic modulator to which the present invention is applied. The communication pulse light source of the present embodiment includes a semiconductor laser 14, an isolator 15 having a return light removal function, a resonator composed of a pair of mirrors 16 and 18, an optical phase modulator 17 inserted in the resonator, In addition to the microwave generator 11, a variable microwave attenuator 12 and a microwave amplifier 13 are provided on the microwave input side of the Fabry-Perot electro-optic modulator.

  FIG. 2A shows a configuration example of the variable microwave attenuator 12 that can change the modulation index at high speed. The variable microwave attenuator 12 includes an input side diode switch 121 having 1 input and n output (n is an integer of 2 or more), an output side diode switch 122 having n input and 1 output, and both diode switches 121, There are n fixed microwave attenuators 123 having different attenuation amounts connected to the respective channels of the switches between 122, and a TTL signal (transistor, transistor, logic signal) from a personal computer (not shown). Is input to a pair of diode switches 121 and 122, and the channel through which the microwave propagates is switched between the diode switches 121 and 122, so that the voltage amplitude of the microwave from the microwave generator 11 is about 20 ns. Can be variable with speed.

  The insertion loss due to the variable microwave attenuator 12 is compensated by the microwave amplifier 13 which can hold the level difference of the input microwave and can be amplified at a constant rate. The relationship between the TTL signal and the microwave output at this time is shown in FIG.

  The TTL signal switches the channel through which the microwave propagates between a pair of diode switches 121 and 122. For example, the microwave output propagating through the fixed microwave attenuator L1 of FIG. 2B at a certain time T0 is propagated through the fixed microwave attenuator L2 by the TTL signal at the time T1. When the diode switches 121 and 122 are switched synchronously, the microwave propagating between the diode switches 121 and 122 propagates through the fixed microwave attenuator 123 that varies depending on the time, so that the voltage amplitude changes depending on the time.

  Strictly speaking, at time T1, the falling of the microwave propagating through the fixed microwave attenuator L1 (about 20 ns) and the rising of the microwave newly propagating through the fixed microwave attenuator L2 (about 20 ns) ) Occur at the same time, impedance mismatch occurs due to the overlapping of the microwaves, and the microwave output from the output side diode switch 122 is significantly reduced for about 20 ns. Therefore, in the pulse width variable light source of the present invention, when outputting at a certain pulse width for T time, it is necessary to set the duration of the TTL signal to (T + 20 ns).

  The microwave output can be made variable at an arbitrary attenuation ratio by setting the attenuation amounts of the n fixed microwave attenuators L1 to Ln. In the variable microwave attenuator 12, reflection due to impedance mismatching occurs, so that reflected microwave waves such as an isolator (not shown) are removed before the diode switch 121 on the incident side and behind the diode switch 122 on the emission side. Preferably, a filter is provided.

(Second Embodiment)
FIG. 3A shows a configuration of a second embodiment of a pulse light source for communication constituted by a Fabry-Perot electro-optic modulator to which the present invention is applied. The communication pulse light source of this embodiment includes a semiconductor laser 14, an isolator 15, a resonator composed of a pair of mirrors 16 and 18, an optical phase modulator 17 inserted in the resonator, and a microwave generator 11. Thus, an optical filter 19 is provided on the output side of the Fabry-Perot electro-optic modulator.

  The optical filter 19 is, for example, a band pass filter that can pass only the long wavelength side (or the short wavelength side) with respect to the wavelength of the incident light, as shown in FIG.

  As a result, the optical pulse train originally having a period of 1/2 fm as shown in FIG. 14A is reduced to half as shown in FIG. Only the optical pulse whose wavelength is shifted to the long wavelength side (or the short wavelength side) with respect to the above wavelength. Therefore, when the optical pulse train generated by the Fabry-Perot electro-optic modulator of this embodiment is passed through an optical fiber (not shown) having wavelength dispersion, the propagation characteristics of the optical pulse are not different between adjacent pulses, and the optical pulse train No deviation in pulse timing occurs even after passing through the optical fiber. Further, even if the optical pulse train generated by the Fabry-Perot electro-optic modulator of this embodiment is passed through the optical amplifier, the amplification characteristics of the optical pulse are not different between adjacent pulses, so that the intensity of the pulse is modulated. Nor.

(Third embodiment)
FIG. 5 shows a configuration of a third embodiment of a communication pulse light source constituted by a Fabry-Perot electro-optic modulator to which the present invention is applied. The communication pulse light source of this embodiment includes an arrayed waveguide grating 20 on the output side of the Fabry-Perot electro-optic modulator in addition to the configuration of the first embodiment of the present invention shown in FIG.

The arrayed waveguide grating 20 is, for example, a bandpass filter that can pass only the long wavelength side (or short wavelength side) with respect to the wavelength of incident light. Also in this case, similarly to the optical filter 19, the repetition period of the optical pulse train output from the arrayed waveguide grating 20 is fm as shown in FIG.
In addition, the arrayed waveguide grating 20 can easily have a structure having a plurality of outputs of two or more, and incident light can be separated into a plurality by the frequency difference. For example, by setting the frequency transmission bandwidth of the arrayed waveguide grating 20 to an integral multiple (P × fm) of the modulation frequency of the Fabry-Perot electro-optic modulator, a plurality of pulse trains (repetition frequency fm) as shown in FIG. Can be generated simultaneously from the arrayed waveguide grating 20. Here, FIG. 6 shows a case where the spectrum of the optical pulse generated at the modulation frequency fm = 10 GHz of the Fabry-Perot electro-optic modulator and the transmission bandwidth of the arrayed waveguide grating 20 with 8 outputs is 40 GHz (4 × fm). An example of the calculation result is shown.

  In addition, as shown in FIG. 6, the frequency component shifted to the long wavelength side and the frequency component shifted to the short wavelength side with respect to the CW laser light (center frequency f0) incident on the Fabry-Perot electro-optic modulator are The transmission frequency of the arrayed waveguide grating 20 must be adjusted so that it does not exist within the same frequency transmission band in the arrayed waveguide grating 20. At this time, since the pulse widths of a plurality of pulse trains (eight pulse trains) generated at the same time are inversely proportional to the transmission frequency bandwidth (P × fm = 40 GHz) of the arrayed waveguide grating 20, in order to increase the number of pulse trains to be generated When each transmission frequency bandwidth is narrowed, the pulse width is widened.

  Furthermore, by making the transmission frequency interval of the arrayed waveguide grating 20 coincide with the modulation frequency of the Fabry-Perot electro-optic modulator, a plurality of continuous lights can be generated. In the case where two or more outputs are used by using a frequency-selective filter or interferometer (not shown) instead of the arrayed waveguide grating 20, the output light pulse is separated by the frequency difference in the same manner as described above. By doing so, a plurality of pulse trains having a repetition frequency fm and a plurality of continuous lights can be generated.

(Fourth embodiment)
FIG. 7 shows a configuration of a fourth embodiment of a communication pulse light source constituted by a Fabry-Perot electro-optic modulator to which the present invention is applied. The communication pulse light source of this embodiment includes a semiconductor laser 14, an isolator 15, a resonator composed of a pair of mirrors 16 and 18, an optical phase modulator 17 inserted in the resonator, and a microwave generator 11. Then, a light intensity modulator 22, such as an MZ modulator (Mach-Zehnder interferometer type modulator), is placed on the input side of the Fabry-Perot electro-optic modulator, and its transmission characteristics are synchronized with the modulation of the Fabry-Perot electro-optic modulator. Thus, the phase of the light intensity modulator 22 is adjusted by the phase modulator 21 so that the characteristics shown in FIG. For this synchronization, the microwave from the microwave generator 11 is supplied to the phase adjuster 21 as a synchronization signal.

  In this case as well, the optical pulse output from the communication pulse light source is the same as that shown in FIG. 4 and is reduced by half, and the wavelength on the long wavelength side (or short wavelength side) with respect to the wavelength of the incident light. Becomes only the optical pulse shifted. Therefore, when the optical pulse train generated by the Fabry-Perot electro-optic modulator of this embodiment is passed through an optical fiber (not shown) having wavelength dispersion, the propagation characteristics of the optical pulse are not different between adjacent pulses, and the optical pulse train No deviation in pulse timing occurs even after passing through the optical fiber. Further, even if the optical pulse train generated by the Fabry-Perot electro-optic modulator of this embodiment is passed through an optical amplifier (not shown), the amplification characteristics of the optical pulse are not different between adjacent pulses. No modulation is added.

  Instead of placing the light intensity modulator 22 on the input side of the Fabry-Perot electro-optic modulator, direct modulation of the semiconductor laser 14 may be used, and instead of placing the light intensity modulator 22 on the input side of the Fabry-Perot electro-optic modulator. The structure may be such that the intensity modulator 22 is placed on the output side of the Fabry-Perot electro-optic modulator.

(Fifth embodiment)
FIG. 9 shows a configuration of a fifth embodiment of a communication pulse light source constituted by a Fabry-Perot electro-optic modulator to which the present invention is applied. The communication pulse light source of this embodiment includes a semiconductor laser 14, an isolator 15, a resonator composed of a pair of mirrors 16 and 18, an optical phase modulator 17 inserted in the resonator, and a microwave generator 11. An optical interferometer 23 is provided on the output side of the Fabry-Perot electro-optic modulator.

  The optical interferometer 23 may be a Michelson interferometer, a Mach-Zehnder interferometer, or a Fabry-Perot interferometer. In any optical interferometer, FSR (free spectrum range) is adjusted to 2 fm so that only the even-order component of the modulation sideband component generated for each fm of the output light is transmitted. Alternatively, by adjusting the wavelength of the semiconductor laser 14, only the even-order component of the modulation sideband component generated for each fm of the output light may be transmitted. In this case, the optical pulse interferes with an adjacent pulse and becomes an optical pulse train whose wavelength does not shift to the long wavelength side (or short wavelength side) with respect to the wavelength of the incident light.

  FIGS. 10A and 10B show calculation examples when the optical interferometer 23 is a Mach-Zehnder interferometer, and the delay is adjusted to 1/2 fm. In the case of FIG. 10, it can be seen that the pulse width is halved and the phase does not change as compared with FIG. The transmission spectrum of the interferometer at this time and the pulse spectrum waveform after passing through the interferometer are schematically shown in FIG.

  Further, by making the optical interferometer 23 have a transmission characteristic of FSR = M × 2fm (M is an integer), the repetition frequency of the pulse train can be an even multiple of 2 or more. This is because the repetition frequency of the pulse train matches the frequency interval (M × 2fm) of the frequency components in the pulse due to the Fourier transform.

  Note that an arrayed waveguide grating (not shown) may be provided in place of the optical interferometer 23, and the FSR of the arrayed waveguide grating may be adjusted to M × 2fm, so that the pulse train repetition frequency is 2 or more as described above. Can be an even multiple of.

  As described above, in the pulse light source for communication according to the present embodiment, the propagation characteristics of the optical pulse do not differ between adjacent pulses, and the optical pulse train does not shift in pulse timing even after passing through the fiber. In addition, even if an optical pulse train generated by a Fabry-Perot electro-optic modulator is passed through an optical amplifier (not shown), the amplification characteristics of the optical pulse do not differ between adjacent pulses, so that the intensity of the pulse is modulated. Nor. As shown in FIG. 10A, the pulse width is shorter than that in FIG. 14, which is advantageous for application to soliton communication or the like that requires a short pulse. Further, the pulse width can be reduced as the microwave power applied to the optical phase modulator 17 is increased. However, if the method of this embodiment is used, a shorter pulse width can be obtained with a lower power microwave.

(Sixth embodiment)
FIG. 12 shows a configuration of a sixth embodiment of a communication pulse light source constituted by a Fabry-Perot electro-optic modulator to which the present invention is applied. The communication pulse light source of the present embodiment includes, for example, an isolator 24 having a return light removing function on the output side of the Fabry-Perot electro-optic modulator in addition to the configuration of the first embodiment of the present invention of FIG. .

  The return light removal function has a structure in which the output light has a high transmittance and a low return light transmittance, such as a filter or isolator, or an angle on the output-side end face of the optical resonator so that the return light does not recouple to the optical resonator. It is obtained by providing. Since the Fabry-Perot electro-optic modulator has a structure in which the optical phase modulator 17 is inserted into the Fabry-Perot optical resonators 16 and 18, the output of the communication pulse light source is optical fiber (not shown) using an optical connector (not shown). ), The reflected light at the end face of the connector becomes the return light to the optical resonators 16 and 18 and interferes by recombining with the optical resonators 16 and 18, and the optical resonators 16 and 18 are not connected. It becomes stable and the output of the variable pulse width light source becomes unstable, but it is possible to prevent the output of the variable pulse width light source from becoming unstable by providing a means for removing the return light as in this embodiment. it can.

(Other embodiments)
The embodiment of the present invention described above is merely a specific example, and the present invention is not limited to this. All examples of modifications, replacements, and the like are within the scope of the claims. Included in embodiments of the invention. For example, what combined the structure of each embodiment of this invention is also effective, and is contained in embodiment of this invention.

  INDUSTRIAL APPLICABILITY The present invention can realize a communication pulse light source capable of high-speed pulse width modulation that could not be realized by the prior art, and can be used for optical communication that propagates an optical fiber over a long distance. Since it can be generated and a pulse train having an even multiple of the modulation frequency can be generated stably, it is highly practical and can be expected to have a wide range of applications in high-speed optical fiber network communications.

It is a block diagram which shows the structure of 1st Embodiment of the pulse light source for communication of this invention. (A) is a block diagram which shows the structural example of the variable microwave attenuator which comprises the pulse light source for communication of this invention, (b) shows the relationship between the control signal and microwave output in the variable microwave attenuator. It is a timing diagram. (A) is a block diagram which shows the structure of 2nd Embodiment of the pulse light source for communication of this invention, (b) is a timing diagram which shows typically the spectrum of the output pulse of the pulse light source for communication. It is a wave form diagram which shows an example of the output pulse of the pulse light source for communication of FIG. It is a block diagram which shows the structure of 3rd Embodiment of the pulse light source for communication of this invention. FIG. 6 is a timing chart showing that a plurality of pulse trains having different wavelengths are generated in the communication pulse light source of FIG. 5. It is a block diagram which shows the structure of 4th Embodiment of the pulse light source for communication of this invention. It is a characteristic view which shows the transmission characteristic of the light intensity modulator in the pulse light source for communication of FIG. It is a block diagram which shows the structure of 5th Embodiment of the pulse light source for communication of this invention. (A) is a waveform diagram showing an example of an output pulse of the communication pulse light source of FIG. 9, and (b) is a characteristic diagram showing a relative phase of the output pulse of the communication pulse light source with respect to incident light. FIG. 10 is a timing diagram schematically showing a spectrum waveform of an output pulse of the communication pulse light source of FIG. 9. It is a block diagram which shows the structure of 6th Embodiment of the pulse light source for communication of this invention. It is a block diagram which shows the structural example of the pulse light source comprised with the conventional Fabry-Perot electro-optic modulator. (A) is a wave form diagram which shows an example of the output pulse of the pulse light source comprised by the conventional Fabry-Perot electro-optic modulator, (b) is the output of the pulse light source comprised by the conventional Fabry-Perot electro-optic modulator. It is a characteristic view which shows the relative phase with respect to the incident light of a pulse. It is a characteristic view which shows an example in which the pulse width of an output light pulse changes by control of a modulation index. It is a characteristic view which shows an example of the calculation result showing that the output light pulse of the pulse light source comprised with the conventional Fabry-Perot electro-optic modulator propagates | transmits a fiber, and the timing difference of a pulse generate | occur | produces. It is a characteristic view which shows an example of the calculation result showing that the output light pulse of the pulse light source comprised with the conventional Fabry-Perot electro-optic modulator generate | occur | produces the intensity | strength modulation between pulses by an optical amplifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Microwave generator 12 Variable microwave attenuator 121,122 Diode switch 123 Fixed microwave attenuator 13 Microwave amplifier 14 Semiconductor laser 15 Isolator 16, 18 Mirror (Fabry-Perot optical resonator)
17 Optical Phase Modulator 19 Optical Bandpass Filter 20 Array Waveguide Grating 21 Phase Adjuster 22 Optical Intensity Modulator 23 Optical Interferometer 24 Isolator

Claims (10)

A pulsed light source composed of a semiconductor laser and a Fabry-Perot electro-optic modulator, wherein a voltage amplitude of a modulation microwave driving the Fabry-Perot electro-optic modulator is changed according to a control signal to have a pulse width varying means capable of a pulse width variable,
The variable pulse width means includes a variable microwave attenuator provided on the microwave input side of the Fabry-Perot electro-optic modulator, and the variable microwave attenuator has at least n outputs (n is an integer of 2 or more). And an input side diode switch having at least n inputs, and n fixed microwave attenuators having different attenuation amounts connected to the respective channels of the switches between both diode switches. A pulse light source for communication. The instantaneous optical frequency of the output light pulse of the pulse light source is positive compared to the input optical frequency every second of the output pulse train, or negatively the output light is repeatedly shift, constant frequency shift or frequency shift, 2. The pulse light source for communication according to claim 1, further comprising a frequency adjusting means for making an optical output free from any noise. The frequency adjusting means is provided on the light output side of the Fabry-Perot electro-optic modulator, and can pass only the long wavelength side or the short wavelength side with respect to the wavelength of the incident light. The pulse light source for communication according to claim 2 , which is a filter or an optical bandpass filter. The output optical pulse train of the pulse light source, the optical frequency components by separating, according to claim 1, characterized in that it has a constant frequency shift or frequency adjusting means to two or more light output without the frequency shift, communication pulse light source. The frequency adjusting means is an arrayed waveguide grating provided on the light output side of the Fabry-Perot electro-optic modulator and capable of passing only the long wavelength side or the short wavelength side with respect to the wavelength of incident light. The communication pulse light source according to claim 4 . The frequency adjusting means includes a light intensity modulator provided on the light input side or light output side of the Fabry-Perot electro-optic modulator, and the light intensity modulator in synchronization with the modulation of the Fabry-Perot electro-optic modulator. The pulse light source for communication according to claim 4 , further comprising a phase modulator that adjusts the phase of the light source. A frequency adjusting unit that transmits only the optical frequency component of even multiple of 2 or more of the modulation frequency in the Fabry-Perot electro-optic modulator, and makes the repetition frequency of the optical output pulse an even multiple of 2 or more of the modulation frequency. The pulse light source for communication according to claim 1, wherein: 8. The communication pulse light source according to claim 7 , wherein the frequency adjusting means is an optical interferometer provided on a light output side of the Fabry-Perot electro-optic modulator. Return light blocking means provided on the light output side of the Fabry-Perot electro-optic modulator and functioning so that a return light component of the light output does not recombine with the Fabry-Perot electro-optic modulator. Item 9. The communication pulse light source according to any one of Items 1 to 8 . The return light blocking means has a direction dependency of the transmittance, and has a high transmittance only in the output direction. The isolator, the optical filter, or the angle on the output side end face of the optical resonator of the Fabry-Perot electro-optic modulator The communication pulse light source according to claim 9 , wherein return light is structured not to be recoupled to the optical resonator.

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